The present invention relates to the art of induction heating and, more particularly, to the induction heating and hardening of gear teeth.
The present invention finds particular utility in connection with the induction heating and hardening of gear teeth on a gear which is characterized by a radially extending axially thin hub plate having a plurality of radially thin circumferentially extending flange segments extending thereabout and the teeth of which gear are on the outer surfaces of the flange segments. Accordingly, the invention will be described in detail in connection with a gear of this structure. At the same time, it will be appreciated that the invention is applicable to the hardening of teeth on other gear structures in which the teeth are on a radially thin circumferentially extending flange which may be supported other than by a radially extending circumferentially continuous hub plate.
Gears of the character having a radially extending hub plate supporting radially thin circumferentially extending gear flange segments having teeth on the radially outer sides thereof are of course well known. Such gears are employed for example in the automotive industry as synchronizing gears, the teeth of adjacent segments being circumferentially interrupted as required to provide a desired synchronizing function. In the use of such gears, clearances between the gear and components with which the gear is to be associated are minimal, whereby it becomes extremely important in connection with hardening the gear teeth to achieve a desired hardness pattern therein without distortion of either the teeth contour or the gear flange, either of which can lead to an unacceptable end product. Additionally, for reasons including the economics of production, it is desirable to achieve heating and hardening of a segmental portion of the teeth on such a gear by a noncircling inductor arrangement and by an axially scanning displacement between the inductor and gear for the heating to be axially progressive along the teeth from one axial end of the gear flange toward the other.
Inductors and induction heating units heretofore available for induction heating by such a scanning procedure do not enable satisfactorily achieving a desired hardness pattern along the outer ends of the gear teeth of such a gear without the distortion referred to above. In this respect, for example, the use of such previous equipment has resulted in overheating one end or the other of the gear teeth and thus a deviation from the desired heating pattern therealong. Other problems encountered have included insufficient heating of the teeth at the circumferentially opposite ends of the flange segment, a concave outer tooth surface, and undesirable heating into the flange and hub plate at the circumferentially opposite ends of the flange segment. The latter especially can cause flange distortion at the segment ends resulting in an increase in the outside diameter of the gear in these areas.